1. Field of the Invention
The invention relates generally to a photoreceiver for detecting and amplifying optical signal in an optical communication system of an ultra-high large-scale wavelength division multiplexing mode, and method of manufacturing the same. More particularly, the invention relates to a photoreceiver in which a photodetector using a quantum-well structure having a quantum confined stark effect as an optical absorption layer and a heterojunction bipolar transistor are integrated on a single chip, whereby an optical signal of a specific wavelength is selectively detected and a converted electrical signal is amplified, thus providing a good amplification characteristic and receiver sensitivity, and method of manufacturing the same.
2. Description of the Prior Art
A conventional photoreceiver, which has been widely used in optical communication systems, has a structure in which a p+InGaAs/ixe2x88x92InGaAs/n+InGaAs long wavelength photodetector 10 of a common PiN structure and a heterojunction bipolar transistor 20 of a n+InP/p+InGaAs/ixe2x88x92InGaAs/n+InGaAs structure are integrated on a semi-insulating InP substrate 101, as shown in FIG. 1.
In other words, the long wavelength photodetector 10 has an n+InGaAs layer 102A, an nxe2x88x92InGaAs optical absorption layer 103A and a p+InGaAs ohmic layer 104A, all of which are stacked on given regions of the semi-insulating InP substrate 101. At this time, the nxe2x88x92InGaAs optical absorption layer 103A and the p+InGaAs ohmic layer 104A are formed on a given region of the n+InGaAs layer 102A. A p-electrode 105 is formed on a given region of the p+InGaAs ohmic layer 104A and a n-electrode 106 is also formed on a given region of the n+InGaAs layer 102A.
Also, a heterojunction bipolar transistor 20 has a n+InGaAs sub-collector 102B, a nxe2x88x92InGaAs collector 103B, a p+InGaAs base 104B, an n+InP emitter 108 and a n+InGaAs ohmic layer 108, all of which are stacked. The nxe2x88x92InGaAs collector 103B and the p+InGaAs base 104B are formed on a given region over the n+InGaAs sub-collector 102B. An n+InP emitter 107 and an n+InGaAs ohmic layer 108 are also formed on a given region over the p+InGaAs base 104B. An emitter electrode 109 is formed on the n+InGaAs ohmic layer 108. A base electrode 110 is formed on a given region over the p+InGaAs base 104B. A collector electrode 111 is formed on a given region over the n+InGaAs sub-collector 102B.
Meanwhile, polymer 112 for protecting the surface of the long wavelength photodetector 10 and the heterojunction bipolar transistor 20 and electrically connecting them is formed on the entire structure. The long wavelength photodetector 10 and the heterojunction bipolar transistor 20 are then patterned to expose respective electrodes, thus forming an air bridge metal line between the p-electrode 105 of the photodetector 10 and the base electrode 110 of the heterojunction bipolar transistor 20.
The crystal structure of the p+xe2x88x92InGaAs/ixe2x88x92InGaAs/n+xe2x88x92InGaAs long wavelength photodetector of a simple PiN crystal structure thus constructed, has been widely employed since additional crystal growth for integrated photodetectors are unnecessary because it is same with the base, collector and the sub-collector of the heterojunction bipolar transistor.
The photoreceiver of this structure has only a simple function of detecting and amplifying optical signals but does not have a characteristic of selectively detecting optical signals considering wavelength. Further, there is another problem in the conventional structure. That is, as the layer for absorbing light is the surface incident type, the cross section of an optical fiber is wide and covers all the area of an integrated chip if the structure is made module by using this optical fiber coupling scheme, thus having difficulty in making a module of the structure.
Various wavelengths are multiplexed in a current large-scale wavelength division multiplexing optical communication system. Thus, an optical grating router, an arrangement waveguide diffraction grating, and the like in the receiving element again demultiplexing multiplexed signals. A photodetector then converts the demultiplexed optical signals into electrical signals. Next, an amplifier amplifies the electrical signals. As such, the construction of the receiving elements for demultiplexing, detecting and amplifying the optical signals becomes complex. Therefore, there is a disadvantage that the manufacturing cost is high. Therefore, in order to construct an cost effective optical communication system of a ultra-high long distance large-scale wavelength division-multiplexing mode, there is a need for a photoreceiver for selectively detecting the optical signals of a specific wavelength from various multiplexed wavelengths and having a high gain amplification function of converted electrical signals.
The present invention is contributed to solve the above problems and an object of the present invention is to provide a single chip integrated photoreceiver capable of selectively detecting optical signals of a specific wavelength from various wavelengths and having a function of amplifying converted electrical signals, and method of manufacturing the same.
Another object of the present invention is to provide a single chip integrated photoreceiver in which a waveguide type photodetector using a quantum-well structure having a quantum confined stark effect as an optical absorption layer and a n+InP/p+InGaAs/nxe2x88x92InGaAs/n+InGaAsP heterojunction bipolar transistor for amplifying electrical signals converted by the waveguide type photodetector are integrated on semi-insulating InP substrate, and method of manufacturing the same.
According to the present invention, in order to selectively detect optical signals of a specific wavelength, a waveguide type photodetector using a multiple quantum-well layer having a quantum confined stark effect as an optical absorption layer. As shown in FIG. 2, the wavelength of light that is absorbed by the quantum confined Stark effect the transition energy of which at the optical absorption band is varied depending on the intensity of an electric field applied to the multiple quantum-well layer, as shown in FIG. 2. Therefore, a wavelength selective detection characteristic can be very simply implemented. Further, the waveguide type photodetector of this type is integrated on a single semi-insulating InP substrate with a heterojunction bipolar transistor having an n+InP/p+InGaAs/nxe2x88x92InGaAs/n+InGaAsP high gain amplification characteristic. Therefore, a photoreceiver of a cost effective and high performance having a function of selectively detecting a specific wavelength, which can be used in an optical communication system of a high-performance wavelength division-multiplexing mode, is provided.
In order to accomplish the above object, a photoreceiver according to the present invention, is characterized in that it comprises a waveguide type photodetector consisting of a p+InGaAsP ohmic electrode formed on a given region of a semi-insulating InP substrate, an ixe2x88x92InGaAsP(xcex1)/ixe2x88x92InGaAsP(xcex2) optical absorption layer of a multiple quantum-well structure which are stacked on a given region of the p+InGaAsP ohmic electrode, a n+InGaAsP, an nxe2x88x92InGaAs ohmic layer, and a n-electrode and a p-electrode each of which is formed on a given regions of the nxe2x88x92InGaAs layer and a given region of the p+InGaAsP ohmic electrode; and a heterojunction bipolar transistor consisting of a p+InGaAsP layer stacked on a given region of the semi-insulating InP substrate, ixe2x88x92InGaAsP(xcex1)/ixe2x88x92InGaAsP(xcex2) layer and n+InGaAsP sub-collector layer of a multiple quantum-well structure, nxe2x88x92InGaAs layer and p+InGaAs base layer for high-speed current transfer that are stacked on given regions of the n+InGaAsP sub-collector layer, n+InP emitter layer and n+InGaAs ohmic layer which are stacked on given regions of the p+InGaAs base layer, an emitter electrode formed on the n+InGaAs ohmic layer, a base electrode formed on a given region of the p+InGaAs base layer, and a collector electrode formed on a given region of the n+InGaAsP sub-collector layer.
Further, a method of manufacturing a photoreceiver according to the present invention, is characterized in that it comprises the steps of sequentially forming a p+InGaAsP layer, an ixe2x88x92InGaAsP/ixe2x88x92InGaAsP layer of a quantum-well structure, an n+InGaAsP layer, an nxe2x88x92InGaAs layer, a p+InGaAs layer, an n+InP layer and an n+InGaAs layer on a semi-insulating InP substrate; defining a photodetector region and a heterojunction bipolar transistor and then removing the n+InGaAs layer, the n+InP layer and the p+InGaAs layer in the photodetector region; etching out the given region of nxe2x88x92InGaAs layer, n+InGaAsP layer and the ixe2x88x92InGaAsP(xcex1)/ixe2x88x92InGaAsP(xcex2) layer of a quantum-well structure in the photodetector region to expose the p+InGaAsP layer, thus defining a waveguide type photodetector; forming a n-electrode on a given region of the nxe2x88x92InGaAs layer and then forming a p-electrode on a given region of the p+InGaAsP layer to produce a waveguide type photodetector; isolating the photodetector region and the heterojunction bipolar transistor region by etching to a given region of the p+InGaAs layer from the n+InGaAs layer to expose a given region of the semi-insulating InP substrate; selectively etching the n+InGaAs layer and the n+InP layer in the heterojunction bipolar transistor region to form an emitter electrode of a mesa shape; forming a base electrode on a given region of the exposed p+InGaAs layer; and removing the nxe2x88x92InGaAs layer and then forming a collector electrode on a given region of the exposed n+InGaAsP layer, thus producing a heterogeneous bipolar transistor.